1. Field of the Invention
The present invention relates generally to a method and apparatus for adding and dropping channels in an optical communications system.
2. Description of Related Art and General Background
In many applications of dense-wavelength division multiplexed (DWDM) optical systems (for example, optical computer networks, CATV (cable television) systems, and telecommunications networks), there exists a need to allow local dropping and adding of traffic carried by one or more wavelengths. Applications include when optical channels are sent to or dropped from an optical transmission line e.g., for sending optical channels to a local bus or for adding local channels to an incoming data signal. This form of optical routing may be generally referred to as xe2x80x9cadd-drop multiplexing.xe2x80x9d
While a basic optical add/drop multiplexer has been described by Taga, et al. (U.S. Pat. No. 5,822,095), it is suited to relatively wide channel spacing and is not suited to modern DWDM systems which tend to have a larger number of more narrow channels which are closely spaced. Mizrahi (U.S. Pat. No. 5,982,518) has proposed one solution for more narrow channels using sequential fiber gratings between optical circulators. In each case, however, a set of local transmitters is required to produce the added channels, increasing the cost and complexity of the add/drop node.
In each of these devices, each transmitter requires the use of a wavelength locker in order to maintain the wavelength stability of the transmitted channels. Such wavelength lockers are available which allow wavelength stability of between about 2.5 GHz and 5 GHz. However, such tolerances are only effective for use in networks having a channel spacing of about 50 GHz. When channel spacing is below about 10 GHz, currently available wavelength lockers are too imprecise to allow transmission without any interference between channels.
Embodiments of the present invention address the needs identified above and others by providing a method of optical data transmission including receiving an optical signal having a plurality of components, each component having a different wavelength, receiving an information signal, separating a first one of the components from the optical signal, dropping a second one of the components from the optical signal, modulating the first one of the components with the information signal to obtain a modulated component, and combining the modulated component with the optical signal.
Another embodiment of the present includes an add/drop device for optical data transmission including an optical waveguide configured and arranged to receive a signal having a plurality of components, each component having a different wavelength, a splitter coupled to the optical waveguide and configured and arranged to produce a first output signal and a second output signal, each output signal having the plurality of components, a first filter configured and arranged to separate a first one of the components from the first output signal, a modulator configured and arranged to modulate the first component with an information signal, a second filter configured and arranged to drop a second one of the components, different from the first component, and a combiner configured and arranged to combine the modulated first component with the filtered second output signal.
Yet another embodiment of the present invention includes a dense wavelength division multiplexed optical transmission system, including a transmitter, an optical waveguide configured and arranged to receive an optical signal from the transmitter through the transmission line, the signal having a plurality of components, each component having a different wavelength, a splitter coupled to the optical waveguide and configured and arranged to produce a first output signal and a second output signal, each output signal having the plurality of components, a first filter configured and arranged to separate a first one of the components from the first output signal, a modulator configured and arranged to modulate the first component with an information signal, a second filter configured and arranged to drop a second one of the components, different from the first component, a combiner configured and arranged to combine the modulated first component with the filtered second output signal, and a receiver in optical communication with the combiner.